In general, wheel bearing apparatus that can rotationally support a wheel hub for mounting a wheel, via double row rolling bearings, is classified for a driving wheel and a driven wheel. For structural reasons, the wheel bearing apparatus of an inner ring rotation type is used for the driving wheel. Both the inner ring rotation type and outer ring rotation type are used for the driven wheel. In general, the wheel bearing apparatus is classified as a so-called first through fourth generation type. In the first generation type, the wheel bearing has double row angular-contact ball bearings fit between the knuckle and the wheel hub. In the second generation type, a body mounting flange or a wheel mounting flange is integrally formed on the outer circumference of an outer member. In the third generation type, one of inner raceway surfaces is directly formed on the outer circumference of a wheel hub. In the fourth generation type, the inner raceway surfaces are directly formed on the outer circumferences, respectively, of the wheel hub and the outer joint member of a constant velocity universal joint.
The wheel bearing apparatus is provided with seals to prevent leakage of grease contained within the bearing apparatus and entry of rain water or dust from the outside of the bearing apparatus. Recently, there is a desire for the bearing apparatus to have a long durability and be maintenance free during the life of an automobile. Under these circumstances, it has been found that many causes of trouble are based on bearing seals due to entry of rain water or dust into the bearing rather than peeling or breakage of structural elements of the bearings. Accordingly, it is very important to improve the sealability of the bearing apparatus in order to extend its life.
Several seals improvements have been proposed with increased sealability and one example of the seals of the prior art is shown in FIG. 8. This seal 50 is mounted in one opening of an annular space formed between ends of an outer member and an inner ring. The seal 50 has an annular slinger 51 and an annular sealing plate 52 arranged opposite to each other. The slinger 51 is press-formed from steel sheet with a substantially L-shaped longitudinal section. It has a cylindrical portion 51a, press-fit onto the inner member (inner ring, not shown), and a standing portion 51b extending radially outward from the cylindrical portion 51a. 
The sealing plate 52 has a substantially L-shaped longitudinal section. It includes a metal core 53 and a sealing member 54. The metal core 53 is press-fit into the outer member (not shown). The sealing member 54 is adhered to the metal core 53, via vulcanizing adhesion. The sealing member 54 is formed of elastic material and includes a pair of side lips 54a, 54b and a grease lip 54c. The side lips 54a, 54b are in sliding contact with the standing portion 51b of the slinger 51. The grease lip 54c is in sliding contact with the cylindrical portion 51a of the slinger 51. The side lips 54a, 54b radially extend angularly outward and their tip ends are in sliding contact with the standing portion 51b of the slinger 51, via a predetermined interference. In addition, a magnetic encoder 55 is integrally adhered to the side surface of the standing portion 51b of the slinger Si, via vulcanizing adhesion.
In this case, if a distance C between the pair of side lips 54a, 54b is set to 0.1 mm or more, the sectional height H of the seal 50 could be reduced to about 6 mm without detracting from the muddy water resistance. Thus, the weight and size of the wheel bearing can also be reduced (e.g., see JP2009-127790A).
High performance can be achieved against muddy water entering into the inside of a wheel bearing by such a prior art seal 50. However, it is difficult to have high performance against muddy water under severe circumstances where the fitting portions, between the seal 50 and the outer member as well as between the outer member and the knuckle where the outer member is fit and directly exposed to the muddy water.
The seal 56 shown in FIG. 9 improves sealability between an outer member 58 and a knuckle 66. Similar to the seal 50 described above, this seal also includes an annular slinger 59 and a sealing plate 60 arranged opposite to each other. They are mounted onto an inner ring 57 and the outer member 58, respectively, to seal the annular space between the inner ring 57 and the outer member 58.
The slinger 59 is press-formed from a steel sheet and includes a cylindrical portion 59a and a standing portion 59b. The cylindrical portion 59a is press-fit onto the outer circumference of the inner ring 57. The standing portion 59b extends radially outward from the cylindrical portion 59a. A magnetic encoder 61, formed from rubber magnet, is integrally adhered to the side surface of the standing portion 59b of the slinger 59, via vulcanizing adhesion. The magnetic encoder 61 is magnetized with N and S poles alternately arranged along its circumference. The magnetic encoder 61 forms a rotary encoder to detect the rotation speed of a wheel.
The sealing plate 60 is press-formed from a steel sheet. It has a metal core 62 and a sealing member 63. The metal core 62 is press-fit into the outer member 58. The sealing member 63 is adhered to the metal core 62, via vulcanizing adhesion. The sealing member 63 is formed of elastic material, such as rubber or synthetic resin. The sealing member 63 has a side lip 63a and a pair of radial lips 63b, 63c. The radial lips 63b, 63c are in sliding contact with the cylindrical portion 59a of the slinger 59. The standing portion 59b of the slinger 59 opposes the outer circumference of the sealing member 63 via a slight radial gap and forms a labyrinth seal 64.
In addition, an edge portion of the outer circumferential end of the sealing member 63 is formed with a radially outward extending outer circumferential lip 65. The outer circumferential lip 65 has a L-shaped longitudinal section and is adapted to be fit in a gap “e” between the outer member 58 and the knuckle 66. Thus, it is possible to seal the gap “e” and prevent muddy water, etc. from entering into the gap “e”. Accordingly, the generation of corrosion on the outer member 58 and knuckle 66 is prevented (e.g. see JP2003-56579A).
However, in such a prior art seal 56, the outer circumferential lip 65 cannot surely contact with the knuckle 66 and the outer member 58 at two points, i.e., at the lip apex 65a and the tip end 65b, if the bent angle of the tip end portion 65b is not properly set. That is, if the bent angle of the tip end portion 65b is not properly set, the outer circumferential lip 65 would be curled and thus collapse between the end face of the outer member 58 and the knuckle 66. This would cause an unsealed gap between the outer member 58 and the knuckle 66. Thus, the reliable sealability cannot be achieved.